13. Lateral Force Coefficient
V = (Z I K C S) W = α W
• V : Base Shear
• Z : Seismic Zone Factor
• I : Occupancy Importance Factor
• K : Horizontal Force Factor (ductility factor)
• C : Period Coefficient
• S : Soil Profile Coefficient
• W : Weight of structure
UBC 85
17. Z-FACTOR
• ZONE 0 Z = 0
• ZONE 1 3/16
• ZONE 2 3/8
• ZONE 3 3/4
• ZONE 4 1
UBC 85
18. I-FACTOR
• Essential Facility 1.50
• Assembly Buildings 1.25
• Normal Buildings 1.00
• Essential facilities: Those buildings which must be
safe and usable for emergency purposes after an
EQ in order to preserve the health and safety of
general public.
• Assembly Building: Any building where the
primary occupancy is for assembly use for more
than 300 persons in one room.
UBC 85
19. K-FACTOR
• Building with shear wall and without a vertical
moment resisting frame 1.33
• For braced frame systems 1.00
• Dual combination of frame and braced frames or
shear wall 0.80
• Ductile Moment Resisting Space Frame 0.67
UBC 85
22. Soil Profile : S1
• Rock of any characteristic, either shale-like or
crystalline in nature.
• Such material may be characterized by a shear
wave velocity greater than 2500 ft/sec;
• Stiff soil conditions where the soil depth is less
than 200 ft and the soil types overlaying rock are
stable deposits of sands, gravel or stiff clays.
UBC 85
23. Soil Profile : S2
• Deep Cohesion-less or stiff clay soil
conditions; including sites where the soil
depth exceeds 200 feet and the soil types
laying rock are stable deposits of sands,
gravels or stiff clays.
UBC 85
24. Soil Profile : S3
• Soft to medium-stiff clays and sands
• Characterized by 30 feet or more of soft to
medium stiff clay with or without intervening layers
of sand or other cohesion-less soils;
• Stiff soil conditions where the soil depth is less
than 200 ft and the soil types overlaying rock are
stable deposits of sands, gravel or stiff clays.
UBC 85
25. S
Where time period of soil Ts is known
For T ≤ Ts
UBC 85
2
1.00 0.5
s s
T T
S
T T
= + −
26. S
For T ≥ Ts
UBC 85
2
1.20 0.60 0.3
s s
T T
S
T T
= + −
27. W
• W is total dead load of structure.
Includes 25% of live load as well for the
storage and warehouse occupancies
Weight of snow, where design snow load is
greater than 30 psf, is included
Weight of snow may be reduced to 75% if
the snow load duration is short.
28. DISTRIBUTION OF LATERAL FORCE
1
n
t i
i
V F F
=
= + ∑
0.07 ; for > 0.7; 0.25t tF TV T F V= ≤
∑=
−= n
i
ii
xx
tx
hW
hW
FVF
1
)(
UBC 85
F1
F3
Fx
V
F2
Fn+Ft
Wx
Wn
W1
hx
n
x t i
i x
V F F
=
= + ∑
( ) ( )
n
x t n x i i x
i x
M F h h F h h
=
= − + −∑
